Processes for preparing a flexible polyurethane foam by reacting a polyisocyanate, one or more polyether polyols and water have been described widely.
Flexible polyurethane foams often do not have sufficient load-bearing properties. In order to provide such foams with enhanced load-bearing properties often polyols are used which contain particulate materials dispersed therein. Examples of such polyols are so-called SAN-based polymer polyols, PIPA-polyols and PHD-polyols. If the particulate material has particles with a rather big average particle size (micron-sized particles), only a low surface area and limited interfacial interaction per weight unit is achieved. As a consequence of the low surface area and limited interfacial interaction only a low potential for mechanical reinforcement per weight unit may be achieved.
In the prior art, polyurethane/polyurea particles, in particular polyurethane/polyurea nano-particles are disclosed. As an example, US2006/0128885A1 discloses a method to make polyurethane-polyurea particles having two discrete maxima in the particle size distribution, consisting of at least two discrete steps, performed in batch mode. In a first step, amines carried in water are added to a prepolymer, i.e. the reaction product of polyisocyanate and a polyol, which polyisocyanate is carried in acetone. After the initial reaction, water is added to complete the forming of polyurethane-polyurea particles. In a further step, the large amount of acetone is to be evaporated
EP 418039 discloses a process for preparing PIPA-polyol and a process for preparing flexible polyurethane foams using such PIPA-polyol. The PIPA particles have a size falling into two discrete ranges of 100-700, preferably 100-400 and more preferably of 100-200 nm on the one hand and of 200-more than 1000, preferably up to 1000, more preferably up to 800 nm on the other hand. Example 2, sample 7 showed a particle size of 800 and of more than 1000 nm. When the experiment was repeated the average particle size was determined at 1.7 μm.
The formation of relatively small (up to 0.3 μm) urea aggregates in flexible polyurethane foam preparation in itself is known; see Journal of Applied Polymer Science, Vol. 35, 601-629 (1988) by J. P. Armistead et al. and Journal of Cellular Plastics, Vol. 30, page 144, (March 1994) by R. D. Priester et al.
Until recently it was believed that by increasing the urea hard phase content other important properties like resiliency, hysteresis and compression set will suffer; see Polyurethanes Expo '98, 17-20 Sep. 1998, page 227 by D. R. Gier et al.
EP1305352, discloses in-situ formed particulate material having a relatively large average particle size and comprising urea and urethane groups.
The state of the art particulate materials are particles having polyurethane and polyurea groups, have rather large particle diameters and rather non-uniform particle size distribution which gives limitation towards their applicability as reinforcement additives in formulations used to make up a polyurethane foam. The limited effect is due to a significant smaller surface area and hence interfacial interaction with the (foam) matrix and also the process for forming the foams may be negatively influenced.
The process for forming the foams is more likely to be influenced with particulate materials with small particle diameters, because of the large surface area.